This invention relates to a jointed support system and methods to construct the same. More particularly, this invention relates to molding processes and methods of constructing many different types of support systems and structures at a relatively low cost and from a number of discrete components.
For convenience of description, the invention will hereinafter be described, by way of example, in terms of a skeleton for a doll, a figure or toy. However, it should be understood that the invention applies equally well to many different types of devices. Some of these devices may be used for leisure or recreational devices such as toys, play jewelry, or the like. Another use of the invention might be industrial, as, for example, making a hollow spout for a gas can. Other of these devices may be utilitarian, such as a chain, stand, or the like.
An object of the invention is to provide a method of constructing structures from molded plastic parts which are produced at a reasonable cost from the fewest number of different part designs. For example, a chain might be made from only two types of discrete parts which can be snapped together. These same two types of parts may be used to make the skeleton of a toy.
Another object of the invention is to provide a method which enables a reduced cost for assembly by minimizing the required hand assembly. Here, an assembly machine should have general utility to assemble different types of parts into any of many different configurations.
Yet another object of the invention is to provide devices having a wide ranging freedom of movement in order to make jointed, movable structures. For example, a doll or toy should be able to move its body and limbs with a degree of freedom which is approximately the same degree of freedom enjoyed by the animal represented by the doll or toy.
A further object of the invention is to provide a jointed structure which may be easily moved to a particular position or posture, where it will remain, without unwanted movement until it is deliberately moved again.
In keeping with an aspect of the invention, a preferred embodiment has just two basic types of parts. First, there is a rod having a ball on each end to create a shape similar to the shape of a dumbbell. A second discrete part is a sleeve in the form of a cylinder having a central bore with an undercut region near each end of the bore to form a socket. One ball of the dumbbell shaped part is pressed into the bore of a sleeve where the ball is captured in the undercut region in order to form a ball and socket joint. A series of these two types of ball and socket parts can be joined to make a linkage of any suitable length.
If the sleeve is to be manufactured at a reasonable cost and with a reasonable lifetime, the injection molded plastic part must be ejected from the mold without loss of its memory in the undercut area despite the fact that the still hot plastic part is pushed out of the mold. Over the lifetime of the sleeve, it should retain its plastic memory so that the joint retains both its freedom of movement and the degree of friction in the joint that preserves the posture of the joint until it is next moved deliberately. These features are accomplished by using a plastic which has a better memory and an appropriate flexibility characteristic so that it enables the sleeve to be ejected from the mold after the in-mold cooling and retains its memory afterward. The mold for making the sleeve opens in two steps, a first of which steps enables the plastic to cool somewhat inside the mold cavity before a pin is pulled from the undercut region as the mold opens completely in its second step.